As the atmosphere depletes, the Earth, released from all that pressure, is becoming physically larger. Few people realize that the natural size of this planet is approximately that of Neptune, and that only the pressure of miles of atmosphere keeps it compressed to its current size.

The balance is precarious...only a small reduction would allow Earth to expand considerably, possibly to its full size. Even a small expansion spreads the atmosphere thinner, reducing its pressure further. It's a runaway effect.

As the Earth grows, the crust will crack and expand along current rifts, but the oceans will quickly cool the new crust in most places. Areas where rifts are on land might be a problem.

The oceans will become much shallower as the Earth grows larger (Neptune has about 14 times Earth's surface area). The average depth of Earth's oceans is about 12,000 feet. If the ocean floor were uniform, the average depth of the oceans spread out over 14 times the area would about 850 feet. In reality, in our new, larger world (which I have dubbed "Terra Venti") some isolated parts would be deeper, and a lot of ocean bed would be dry, forming new land or even new continents.

The same mass of Earth, expanded by almost 4 times the diameter, will reduce gravity considerably at the surface, even less than that of the Moon. Since the mass of the Earth is the same, the Moon's orbit will not change, although the distance from the Earth's surface to the Moon will be about 11,000 miles less.

The remaining atmosphere will probably be too thin to support life (a rough calculation shows an equivalent of the present-day atmosphere at about 60,000 feet) and the lower gravity won't help that much.